Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$17.89	6.756%	$19.0986	$19.10	$19.10	$19.10
Purchase #2	$89.89	12.650%	$101.2611	$101.26	$101.25	$101.30
Purchase #3	$79.86	13.107%	$90.3273	$90.33	$90.35	$90.30
Purchase #4	$206.37	12.371%	$231.9	$231.90	$231.90	$231.90
Purchase #5	$58.77	6.474%	$62.5748	$62.57	$62.55	$62.60
Purchase #6	$109.84	4.113%	$114.3577	$114.36	$114.35	$114.40
Purchase #7	$73.26	12.817%	$82.6497	$82.65	$82.65	$82.60
7 purchase totals =	$635.88		$702.1692	$702.17	$702.15	$702.20